Molding apparatus with additive metering and mixing means

ABSTRACT

An apparatus for metering and mixing dry particulate additive with a dry particulate plastic material prior to heating the mixture and molding or injecting the same to form a finished article. The apparatus includes a vertically disposed feed throat tube through which the plastic material is adapted to be fed downwardly into the processing machine. A horizontally directed tubular member extends into the feed throat tube for delivering the additive, the tubular member including vertically aligned upper and lower openings and an open forward end positioned within the feed throat tube. By this arrangement, a portion of the plastic material enters the tubular member through the upper opening and is mixed with the additive therein, and the mixture falls through the lower opening and the open forward end of the tubular member.

This application is a division of copending U.S. application Ser. No.309,950 filed Nov. 27, 1972, and now U.S. Pat. No. 3,827,678.

The present invention relates to an additive metering apparatus for aplastic processing machine, such as an injection molding machine,extruder, or the like.

In plastic processing machines of the described type, it is commonpractice to pre-mix various additives, such as a powdered colorant,ultraviolet absorber, stabilizer, or the like, with the particulateplastic material prior to the molding operation. Such pre-mixing isoften unsatisfactory however, since it is difficult to tell withcertainty whether the amount of the additive being introduced willproduce the desired effect in the finished product. Thus for example,where a specific color is desired in a molded article, there is no wayto check on the effectiveness of the amount of colorant being introducedinto the plastic material until the molding operation is commenced and amolded product is produced. Usually, such production does not startuntil after the pre-mixing is completed, and thus any correction in theamount of additive introduced requires a duplication of the pre-mixingoperation.

To remedy the above difficulties associated with pre-mixing, it has beenproposed to introduce the additive into the plastic material in the feedthroat tube of the molding apparatus and just prior to entering theheated barrel of the apparatus. Thus the mixing of the various materialsoccurs essentially within the barrel and while the materials are beingmelted. It has been found, however, that such limited mixing is ofteninsufficient to obtain a uniform finished product.

It is accordingly an object of the present invention to provide anapparatus for continuously metering a dry additive into a moving streamof dry particulate plastic material while concurrently mixing theadditive with the plastic material.

It is another object of the present invention to provide an additivemetering and mixing apparatus in association with a plastic processingmachine such as an injection molding apparatus, and which is designed toprovide a thorough mixing of the ingredients prior to the ingredientsentering the heated barrel of the machine, and without the pre-mixingrequired heretofore.

It is a more specific object of the present invention to provide anadditive mixing and metering apparatus of the described type wherein aportion of the plastic material is co-mingled and mixed with theadditive within the additive delivery tube such that mixed additive andplastic material is introduced into the moving stream of the plasticmaterial rather than pure additive.

These and other objects and advantages of the present invention areachieved in the embodiment illustrated herein by the provision of anapparatus which includes a vertically directed feed throat tube, and ahopper for directing a dry particulate plastic material downwardly intothe feed throat tube. A tubular member extends horizontally into thefeed throat tube for introducing the additive, the tubular memberincluding an upwardly facing inlet opening and outlet opening meanspositioned within the feed throat tube. As the additive is conveyedthrough the tubular member and into the feed throad tube, a portion ofthe plastic material enters the tubular member through the inlet openingand is mixed therein with the additive. The mixture of the additive andplastic material in the tubular member is then delivered into the feedthroat tube through the outlet opening means.

Some of the objects of the invention having been stated, other objectswill appear as the description proceeds, when taken in connection withthe accompanying drawings, in which --

FIG. 1 is a schematic representation of a plastic injection moldingapparatus embodying the features of the present invention;

FIG. 2 is a fragmentary sectional isometric view of the interior of thefeed throat tube and showing the terminal end portion of the tubularmember for delivering the additive;

FIG. 3 is a view similar to FIG. 2, but with the feed auger in thetubular member deleted for purposes of illustrating the downwardlyfacing outlet opening in the tubular member;

FIG. 4 is a fragmentary top plan view of the terminal end portion of thetubular member and taken in the direction of arrow 4 in FIG. 3.

Referring more specifically to the drawings, the present invention isillustrated in association with a plastic injection molding apparatuswhich is indicated generally at 10 in FIG. 1. As will become apparenthowever, the present invention is equally applicable for use with otherplastic processing machines, such as an extruder or blow moldingapparatus. The molding apparatus 10 includes a feed throat tube 12defining an upper entry end 13 and a lower discharge end 14. A hopper 16is mounted above the tube 12 and in communication with the upper end 13,the hopper 16 being adapted to receive a relatively large quantity ofdry particulate plastic material therein such that the plastic materialflows downwardly into and through the tube 12 by gravity.

The lower discharge end 14 of the feed throat tube 12 communicates withthe injection barrel 18 of the molding apparatus, and as inconventional, the barrel 18 is heated by suitable electrical means (notshown) and houses a relatively large reciprocating injection screw 19.The screw 19 is adapted to be cyclically rotated and reciprocated by theconventional drive apparatus indicated generally at 20 acting throughthe shaft 22. A mold cavity 24 communicates with the discharge end ofthe barrel 18 and is designed to cyclically receive a charge of themelted plastic to form a finished molded plastic article.

During operation of the injection molding apparatus 10, the plasticmaterial enters the rear end of the barrel from the feed throat tube 12and is heated and melted therein. During the injection cycle, the screw19 is shifted axially forwardly toward the left as seen in FIG. 1 toinject the melted plastic into the mold cavity 24. During axial movementof the screw toward the right, the screw is rotated to cause forwardmovement of the plastic relative to the screw.

The additive metering and mixing apparatus of the present inventionincludes a tubular member 30 extending horizontally into said feedthroat tube 12 and defining a terminal end portion 32 positioned withinthe feed throat tube, and a rear end portion 34 positioned outside thefeed throat tube. As best seen in FIG. 3, the terminal end portion 32includes an upwardly facing inlet opening 36, a downwardly facing outletopening 37 and an open forward end 38. The upwardly facing inlet openingextends longitudinally along a substantial portion of the length of theterminal end portion, and the downwardly facing outlet opening 37 issubstantially coextensive with the inlet opening 36 in the longitudinaldirection.

An additive hopper 40 is operatively connected to the rear end portion34 of the tubular member 30 for directing the additive into the bore ofthe tubular member. Also, a feed auger 42 is positioned coaxially withinthe bore of the tubular member 30, and a variable speed electric motor44 is designed to rotate the auger at a selected speed to thereby conveythe additive axially therealong and into the feed throat tube 12 at acontrolled rate.

The inlet opening 36 of the tubular member 30 has a generally teardropoutline as seen in FIG. 4, and defines a relatively large openingportion 36a spaced from the open forward end 38, and a relatively smallopening portion 36b communicating with the open end 38. The outletopening 37 comprises a relatively narrow slot portion 37a underlying thelarge opening portion 36a of the inlet opening and outwardly flared sideedges communicating with the open end 38 to define a widened openingportion 37b.

The specific design of the inlet and outlet openings depends somewhat onthe nature of the plastic material flowing downwardly through the feedthroat tube 12, as well as the nature of the additive. For example, theillustrated relatively narrow slot portion 37a of the outlet opening 37is designed to permit a relatively small quantity of a powered additiveto drop therethrough as the additive is being conveyed along the tubularmember 30 by the auger 42. The removal of the additive thus providesroom for a pelletized plastic material to enter the bore of the tubularmember through the relatively large opening portion 36a, and the narrowslot portion 37a of the outlet opening is designed to preclude thepelletized plastic material from dropping therethrough. Thus thematerials are mixed as they are advanced along the tubular member 30,and as the mixture reaches the widened opening portion 37b and the openforward end 38, it drops into the feed throat tube 12. By thisarrangement, it will be apparent that essentially all of the additive ismixed with a portion of the plastic material within the tubular memberand prior to being introduced into the feed throat tube 12. This mixingof the additive and plastic material in the tubular member 30 has beenfound to greatly facilitate the subsequent further mixing of the twomaterials in the barrel 18 to thereby insure a uniform finished product.

In operation, a dry particulate plastic material, in either powered,granular, or pelletized form is positioned within the hopper 16 suchthat the plastic material flows downwardly through the feed throat tube12 and into the barrel 18 of the molding apparatus. Conventionally theplastic material is a natural, uncolored thermoplastic material, and maycomprise for example any of the polyolefins or their copolymers.

A dry particulate additive, which also may be in either powdered,granular, or pelletized form is positioned in the additive hopper 40.Typically, the additive comprises a concentrated colorant in powdered orpellet form, and it may be pre-blended with other additives such as anultraviolet absorbent, a blowing agent, or a stabilizer.

During the molding operation, the drive apparatus 20 operates to rotateand reciprocate the screw 19 within the barrel 18 to cyclically conveythe heated plastic material along the barrel 18, while the variablespeed motor 44 acts to rotate the auger 42 and thereby convey theadditive through the tubular member 30 while mixing the same with theplastic material which enters through the inlet opening 36. The mixtureis then introduced into the feed throat tube 12 in the manner describedabove. The auger 42 is normally rotated at a constant speed which iscoordinated to the volume of plastic material passing through the feedthroat tube 12. Since the speed of the motor 44 is variable, the amountof the additive being introduced into the plastic material may be easilyadjusted during the molding operation to insure the desired results.

In the drawings and specification, there has been set forth a preferredembodiment of the invention, and although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation.

That which is claimed is:
 1. An apparatus for melting and molding dryparticulate plastic material and having provision for continuouslymetering and mixing a controlled amount of a dry particulate additivewith the dry particulate plastic material such that the composition ofthe molded finished product is uniform and may be readily controlled,said apparatus comprisinga vertically directed feed throat tube definingan upper entry end and a lower discharge end, first hopper meansoperatively connected to said entry end of said feed throat tube fordirecting dry particulate plastic material downwardly therethrough, atubular member extending horizontally into said feed throat tube anddefining a terminal end portion positioned within said feed throat tubeand a rear end portion positioned outside said feed throat tube, saidterminal end portion including an upwardly facing inlet opening andoutlet opening means, second hopper means operatively connected to saidrear end portion of said tubular member for directing a dry particulateadditive into said tubular member, means including a feed augerpositioned coaxially within said tubular member for conveying theadditive axially therealong at a controlled rate, whereby a portion ofthe plastic material flowing downwardly through said feed throat tubeenters said terminal end portion through said inlet opening and is mixedwith the additive, and the mixed additive and plastic material in saidterminal end portion is delivered into said feed throat tube throughsaid outlet opening means, means operatively connected to said lowerdischarge end of said feed throat tube for heating the mixed additiveand plastic material received through said feed throat tube andconveying the heated mixture along a horizontal path of travel, and moldmeans for receiving the mixed additive and plastic material from saidheating and conveying means and forming the same into a molded finishedproduct of uniform composition.
 2. The apparatus as defined in claim 1wherein said additive conveying means further includes a variable speedelectric motor operatively connected to said feed auger whereby the rateof delivery of the additive through said tubular member may beselectively controlled.
 3. The apparatus as defined in claim 1 whereinsaid outlet opening means defines a downwardly facing outlet opening andan open forward end, whereby a portion of the co-mingled additive andplastic material in said terminal end portion drops into said feedthroat tube through said downwardly facing outlet opening and theremainder of the co-mingled additive and plastic material in saidterminal end portion is delivered into said feed throat tube throughsaid open forward end.
 4. The apparatus as defined in claim 3 whereinsaid downwardly facing outlet opening is substantially coextensive withsaid upwardly facing inlet opening in the longitudinal direction.
 5. Theapparatus as defined in claim 4 wherein said upwardly facing inletopening has a generally teardrop outline extending longitudinally alonga substantial portion of the length of said terminal end portion anddefining a relatively large opening portion spaced from said openforward end and a relatively small opening portion communicating withsaid open forward end.
 6. The apparatus as defined in claim 5 whereinsaid downwardly facing outlet opening comprises a relatively narrow slotportion spaced from said open forward end and underlying said relativelylarge portion of said inlet opening, and a widened opening portioncommunicating with said open forward end.
 7. The apparatus as defined inclaim 1 wherein said feed auger extends into said terminal end portionof said tubular member and underlies at least a portion of said upwardlyfacing inlet opening.